Medical technologies have provided a variety of devices to investigate and repair vascular maladies. For example, catheters are maneuvered up through the femoral artery and aorta to the heart for injection of radiological dyes, positioning of electrodes, or to install stents. Occasionally, foreign objects, such as loose stents, electrode leads and fragments of guide wires, are left in a blood vessel after a procedure. The objects must be removed, as they can result in sepsis, vessel blockage, infarction, or perforation of the vessel.
One approach to removing a foreign object from a vessel is surgery. An incision can be made in the body near the lodging site of the object and tissue dissected away until the object is reached and withdrawn. The tissues are then stitched back together and healing takes place over the course of several weeks. Such a procedure is not without risk. The surgery may require general anesthesia, with its inherent risks. Important vessels and nerves can be severed during resection of the tissues to reach the site. Infections can set in at the surgical site. Surgery is costly, and many sites are not readily accessible with open surgical methods.
Approaching the foreign object with a catheter through a blood vessel can be far less expensive and risky. A catheter, with some type of grasping or grappling tool tip can be fed through the vessel to the lodging site with the visual aid of a fluoroscope. At the lodging site, the tool is maneuvered into a position where it can secure a hold on the object. The catheter can then be withdrawn, the foreign object in tow. Difficulties can arise, however, when using current catheter tools in this retrieval task.
A hook style tool can be maneuvered around a foreign object in a vessel and used to drag the object out of the vessel. A disadvantage of the hook tool is that it can not reversibly grasp the end of an object. The hook works best in retrieving long flexible objects and objects with eyelets to receive the hook. If an attempt is made to retrieve a short object with a hook, it can slide down the object and slip off the end. Short stiff objects must be dragged along a vessel in a traverse orientation which can scrape or perforate vessel walls. The hook itself can become unreleasably entangled in objects or vessel walls.
Forceps style catheter tools are available with jaws that can open then clamp down to grasp an object. Such forceps design catheters require maneuvering room for the open mouth jaws to engage the object. The jaws do not surround the object, so they can slip away from the grasp. In some situations, prohibitively large designs may be required to provide an adequate grip.
The open loop snare tool is a fine loop that can constrict to grip the end of objects. For example, in U.S. Pat. No. 5,171,233, “Snare-Type Probe” to Amplatz, et al., a loop of wire is provided at the tip of a catheter which is maneuvered over an end of an object to be retrieved. Once the loop encircles the object, loop wires can be retracted into the bore of the catheter contracting the loop to provide a tight grasp of the object. But, if the end of the object is embedded in the wall of the vessel, the loop can not be maneuvered over the end to snare the object. Moreover, if the end of the object becomes lodged against a wall during withdraw, release of the tool may be difficult.
Another type of catheter snare tool is the threaded snare, e.g., as described in U.S. Pat. No. 5,562,678, “Needle's Eye Snare”, to Booker. Here, a hook-shaped closed loop of superelastic wires is advanced from a catheter bore to curl around one side of an adjacent object. Next, a threader wire is advanced from the bore to extend around the other side of the object and between the wires of the loop. When the closed loop wires are withdrawn into the catheter bore, the object is captured in a contracting snare. Such a catheter tool is capable of capturing an object in a snare even if no free end is available. In addition, the hook and threader can be independently advanced and retracted, allowing ready release by retracting the threader, should the object become immovable. Still, difficulties remain in maneuvering the large double wire hook around objects of different shapes and orientations as it advances in a superelastic shape memory curl from the catheter bore. Maneuvering the threader wire can also be difficult since it is not rotatable independent of the hook. Furthermore the large expensive superelastic loop can be difficult to securely assemble onto a positioning wire do to peculiarities of the superelastic material.
In view of the above, a need exists for a catheter snare tool with the small size and versatile maneuverability required to surround foreign objects with diverse shapes and orientations. Benefits could also be realized through catheter snare tool technologies that cost less and are easier to manufacture. The present invention provides these and other features that will be apparent upon review of the following.